The dispensing of compressed gas from a high-pressure storage system to a lower-pressure receiving vessel or tank is known in the art for various applications such as supplying fuel to compressed natural gas (CNG)-powered or hydrogen-powered vehicles. When compressed gas is transferred from a high-pressure storage vessel to a lower-pressure vessel, the temperature of the gas in the system changes as a function of the thermodynamic properties of the gas and the heat transfer characteristics of the system. Dispensing systems may be designed to control these temperature changes to ensure that the gas transfer process is timely and efficient.
Cascade filling processes that employ multiple high-pressure storage vessels to charge a lower pressure-receiving vessel are known in the prior art, as exemplified in Borck U.S. Pat. No. 6,779,568. The '568 patent discloses that, for a constant filling time, the peak temperature of the gas in the receiving tank will be lower when a lower pressure storage vessel is used first during the cascade filling process. Thus, the '568 patent teaches controlling the order in which the storage vessels are utilized based on the difference in pressure within those storage banks.
The prior art also teaches that the temperature rise in a receiving tank can be limited by adjusting the filling rate from the high-pressure storage vessels, especially at the start of the filling process when the rate of temperature increases the greatest, as exemplified in Hwang, et al. U.S. Pat. No. 5,901,758 and Togasawa, et al. U.S. Pat. No. 6,598,624.
A further prior art approach for limiting or controlling the temperature rise in a receiving tank is to utilize additional hardware, such as a heat exchanger to cool the flowing gas stream from the high-pressure storage vessels, upstream of the receiving tank. The use of such additional hardware is disclosed in Sugano, et al. U.S. Pat. No. 6,360,793 and Cohen, et al. U.S. Pat. No. 6,619,336.
High-pressure gas storage and dispensing systems are usually installed outdoors and are subjected to wide ranges of ambient temperatures. Although the above prior art disclosures focus on the thermal impact that the filling process has on the receiving tank, none of those disclosures takes into account, or even recognizes the need to take into account, the impact of ambient temperature on the compressed gas within and leaving the compressed gas storage system during the process of filling a receiving tank. Based on the limitations of these prior art approaches for storing and transferring compressed gas from high-pressure storage systems to a lower-pressure receiving vessel, there is a need in the art for improved methods and systems for controlling the amount of cooling of the compressed gas within the storage system during transfer from the storage system to a receiving vessel based on ambient temperature conditions. This need is addressed by the embodiments of the invention described below and defined by the claims that follow.